His son John was at school, learning about the Nativity, when he had a question for his teacher.
The teacher had no answer.
John tragically died in a traffic accident aged 12, but his memory burns brightly in his father, who will never forget the boy's impressive curiosity.
"Question everything," Walsh wrote.
Walsh had a bundle of questions for more than a decade about Armstrong and played no small part in the doping downfall of the Tour de France star.
Now, in another sport on the other side of the world, there are many serious questions for Essendon and their football department.
The questions fall into two distinct categories.
Firstly, have Essendon players taken banned substances?
If yes, it is the biggest crisis in the game's history. Essendon and the AFL come under the World Anti-Doping Agency code, which is strict on doping offences. We're talking two-year bans, if not more.
If no, the whole game can breathe a massive sigh of relief - but hopefully learn a timely lesson about "pushing the envelope" with training methods.
The second category of questions is vast, but can be summed up as governance.
Or, "what the hell has been going on at Essendon?"
Who knew about the supplements in question and when? Did the board know? Was the whole football department, including coach James Hird, across what was happening?
Were players ordered to sign waivers?
Were the supplements administered away from the club?
Was sports scientist Stephen Dank, AKA "The Pharmacist", under proper supervision while he worked at the club? How was fitness coach Dean "The Weapon" Robinson involved?
Did Essendon really learn about this problem only a day or two before it went to the AFL?
And so on. But you get the picture.
Also, no-one who follows the AFL or works in the industry should be shocked about this.
Think about it - a billion dollar-plus sport, with the attendant massive pressure for success.
People in sports such as cycling and athletics are now looking over the fence at the AFL and grimly thinking "now you know what it's like in the real world".
But be warned - you might not like the answers.